Sorry for not being more thorough. But because I don't know what the problem is and I don't know how to debug it, it leaves me in a position that can't really be described better than what I have already said. The only thing I can request of you is that you install IPC:RUN-0.80.pm and Graphviz.pm and then try to execute a CGI script and display the graph in your browser and see if you can get it to work. If you can't, then you are having the same problem as me.